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Quiz 3
(8 points for each problem; total of 80 points maximum). You must show how a numerical
answer is obtained to get full credit.
1. A researcher wants to test a null hypothesis that left hindleg and left foreleg lengths of deer
are equal. He has a random sample of 10 animals with the following measurements.
Animal
Hindleg,
cm, X1
Foreleg,
cm, X2
d=X1-X2
1
142
2
140
3
144
4
144
5
142
6
146
7
149
8
150
9
142
10
148
Average
X1
138
136
147
139
143
141
143
145
136
146
X2
4
4
-3
5
-1
5
6
5
6
2
Assume X 1 ~ N ( 1 , 2 ), and X 2 ~ N ( 2 , 2 ) .
Select correct answer(s) from the following:
a. The hypothesis testing should be
H 0 : 1 2
H a : 1 2
b. Since X1 and X2 are not independent, the hypothesis testing should be
H0 : d 0
Ha : d 0
c. The hypothesis testing should be
H 0 : 1 2
H a : 1 2
d. The hypothesis testing can be
H0 : d 0
Ha : d 0
2. A researcher believed that there was a difference in the amount of time boys and girls at 7 th
grade studied by using a two-tailed t test. Which of the following is the null hypothesis?
a. Mean of hours that boys studied per day was equal to mean of hours that girls
studied per day
b. Mean of hours that boys studied per day was smaller than or equal to mean of hours
that girls studied per day
c. Mean of hours that boys studied per day was greater than mean of hours that girls
studied per day
d. Mean of hours that boys studied per day was smaller than mean of hours that girls
studied per day
3. A teacher hypothesized that in her class, grades of girls on a chemistry test were the same as
grades of boys. If the probability value of her null hypothesis was 0.56, it suggested:
a. Girls’ grades were higher than boys’ grades
b. Boys’ grades were higher than girls’ grades
c. We failed to reject the null hypothesis
d. The null hypothesis was rejected
4. A researcher randomly selected 16 boys and 16 girls in a high school and then he measured
their weights. The data are listed below:
Frequency
n
Mean (kg)
Variance*
Boys
16
45.5
2.30
Girls
16
40.3
2.30
1 n
( xi M )2 , where M is sample mean .
n 1 i 1
What is the margin of error of the difference in means (use t-distribution)?
*Variance =
5. A research wants to examine whether a series of interventions affects children’s weight. He
has four experimental groups: Group A provides children safe water, group B provides children
supplementary food, group C provides children Vitamin A supplements, and group D provides
nutrition education to the children’s mothers. If he wants to compare the mean of children’s
weights of each group, he need to keep in mind that as he make several comparison, he have a
(an) ____ chance of a Type I error
a. Decreased
b. Increased
c. Identical
d. Double
6. A professor wants to test all possible pairwise comparisons among five means. If we need to
maintain an experiment –wise alpha of 0.05, what is the error rate per comparison after
applying Bonferroni correction?
7. True or False. If a null hyothesis is not rejected by a 2-tailed test, then the null hypothesis
cannot be rejected under a 1-tailed test.
8. _____A researcher conducted a study to investigate effect of weight loss for patients takkng
diet A and diet B. 0 : = vs. 1 : < . The null hypothesis was highly significant
(rejected) at α<0.001. Select all the correct answers.
(a)
(b)
(c)
(d)
The difference for these two diets must be very large.
The difference for these two diets may or many not be large.
One diet is 1000 times nore effective than the other.
One diet is more effective than the other but the magnitude of the effect is not known.
9. Which of the following can increase power?
a. Decreasing standard deviation
b. Increasing standard deviation
c. Increasing both means but keeping the difference between the means constant
d. Increasing both means but making the difference between the means smaller
10. ___ Which of following descriptions are correct under any study condition? Select all that
apply.
a. Increasing the power will increase the probability of type I error
b. Increasing the significance level (i.e. from 0.05 level to 0.01 level) will increase power
c. Decreasing the significance level (i.e. from 0.01 level to 0.05 level) will increase power
d. Increasing power will decrease the probability of type I error
e. Increasing power has no effect on type I error
...
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